# CVE-2021-21727: Denial of service in > Remote attackers can cause denial of service on ZTE ZXHN F623 devices by sending crafted IPv6 packets, requiring firmware updates to mitigate. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** No - **Published:** 29 Mar 2021 - **Updated:** 3 Aug 2024 - **Also known as:** GHSA-8q85-4h38-w789 ## What is CVE-2021-21727? CVE-2021-21727 is a high-severity denial of service vulnerability in , published on 29 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description A ZTE product has a DoS vulnerability. A remote attacker can amplify traffic by sending carefully constructed IPv6 packets to the affected devices, which eventually leads to device denial of service. This affects: ## Which versions are affected by CVE-2021-21727? It affects 1 product. Products: Zte Zxhn F623 Firmware. ## How do I fix CVE-2021-21727? No fix has been published for CVE-2021-21727 yet. Limit exposure of the affected software until one is available. ## Is CVE-2021-21727 being exploited? There is no known exploitation of CVE-2021-21727 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-21727 and fix it if it is affected. What it is: CVE-2021-21727 is a high-severity denial of service vulnerability in , published on 29 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-21727 in the wild and no public exploit code. Affected product: . No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-21727/ (Markdown: https://insights.sbomify.com/CVE-2021-21727/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21727 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21727 - OSV: https://osv.dev/vulnerability/CVE-2021-21727 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-21727/ Summaries are generated and may contain mistakes; the official description above is the record.